% description X=sigma=volatility
% Black scholes model for put option
function fun=fput(x)
K=1180;
S0=1080.58;
r=0.0075;
T=3/12;
p=109.75;
d1=(log(S0/K)+(r+(x*x./2)*T))./(x*sqrt(T));
d2=d1-x*sqrt(T);
fun=K*exp(-r*T)*cndf(-d2)-S0*cndf(-d1)-p;